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Introduction to Parasites and Parasitic Infections Introduction to Parasites and Parasitic

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Introduction to Parasites and Parasitic Infections Introduction to Parasites and Parasitic Powered By Docstoc
					Introduction to Parasites and
     Parasitic Infections
         Dr. David Haldane
              473-2392
  david.haldane@cdha.nshealth.ca
                 Parasites
•   Eukaryotic
•   Distinct from Fungi
•   No chlorophyll
•   Mixed group of organisms from protozoa
    to helminths
                Types of parasites
• Protozoa
    –   Single celled, Organized cellular structure
    –   May ingest solid particles
    –   Require aquatic environment
    –   Reproduce by binary fission at some point in life cycle
• Helminths (worms)
    – Multicellular, Organized internal structure; includes
         • Platyhelminths (flatworms)
         • Nematoda (roundworms)
•       Ectoparasites
    – Insects and arachnida found on the skin.
     Classification, disease and
       detection of parasites
• Protozoa (based on means of locomotion)
  – Amoebae
    • Form cytoplasmic protrusions (pseudopodia).
    • Occur as trophozoites (active, growing) and cyst
      (environmentally protected) forms.
      Classification, disease and
     detection of parasites (cont’d)
• Pathogens
  – Entamoeba histolytica
• Disease - Ranges from: asymptomatic,
  diarrhea to dysentery and liver disease.
• Transmission - Fecal-oral - contaminated
  water/food, (especially in the tropics).
  – Poor living conditions.
 Note: There is a morphologically identical non-pathogenic
 species called Entamoeba dispar. It is distinguished on the basis
 of clinical history / findings.
       Classification, disease and
      detection of parasites (cont’d)
•   Flagellates
    – Propelled by flagella.
    – May occur in trophozoites and cyst forms.
    – Have shape because of rigid outer wall.
•   Pathogens - Giardia lamblia
•   Disease - Ranges from asymptomatic to
    acute or chronic diarrhea
•   Transmission - Fecal-
    oral,waterborne,World wide.
     Classification, disease and
    detection of parasites (cont’d)
• Trichomonas vaginalis
  – Disease - Vaginitis.
  – Transmission - Sexual.
  – Detection - Microscopy of discharge, culture.
     Classification, disease and
    detection of parasites (cont’d)
• Trypanosoma spp
  – Cause Trypanosomiasis (Sleeping sickness -
    Africa; Chagas Disease - South America)
  – Disease - Fever, encephalitis; cardiac
    complications (Chagas Disease).
  – Transmission - Tse-Tse fly (Africa), Reduvid
    Bug (South America).
  – Detection - Parasites stained on blood
    smears, serology.
     Classification, disease and
    detection of parasites (cont’d)
• Sporozoa
  – Mature forms are non motile.
  – Complex life cycles.
  – Pathogens - Plasmodium spp. Cause malaria.
  – Disease - Episodic fevers, anaemia - life
    threatening!
  – Transmission - Mosquito bites.
  – Detection: - Parasites stained on blood film.
     Classification, disease and
    detection of parasites (cont’d)
• Cryptosporidium parvum
  – Disease: - watery diarrhea (chronic in
    immunosuppressed)
  – Transmission: - fecal-oral, water borne,
    animals (zoonosis), world wide distribution
  – Detection: - microscopy of stool using special
    stains
     Classification, disease and
    detection of parasites (cont’d)
• Cyclospora cayetanensis
  – Disease - Watery diarrhea, similar to above.
  – Transmission - Fecal - oral, especially in
    tropics, outbreaks have occurred in North
    America.
  – Detection - As for Cryptosporidium.
     Classification, disease and
    detection of parasites (cont’d)
• Toxoplasma gondii
  – Disease - Mostly asymptomatic infection, but
    new infection in pregnancy causes fetal
    malformations; also infection in immuno-
    suppressed.
  – Transmission - By poorly cooked meat, from
    cat stool, rarely water.
  – Detection - By serology.
     Classification, disease and
    detection of parasites (cont’d)
• Helminths
  – Platyheminths (flatworms)
    • Cestodes – “tapeworms”
       – Ribbon like, segmented. No digestive system, adult
         attached to gut wall by scolex, larval forms in tissues.
       – Life cycle Definitive Host (gut contains adult worms)
       – Environment (Ova)
       – Intermediate Host (tissues contain larval stage)
       – When the intermediate host is eaten by the definitive
         host, the adult worm develops in the gut from the larval
         form, and later produces ova....
     Classification, disease and
    detection of parasites (cont’d)
• Principle Pathogens
  – Taenia saginata,Taenia solium
     • Disease: - Abdominal discomfort (man is definitive
       host {i.e. has adult}).
     • Transmission: - Larval forms ingested in food.
     • Detection: - Identification of ova or adult segments
       in stool.
  – Some cestodes infect humans by the adult
    form in the gut, some infect by larval forms in
    tissues, and some infect in both forms.
   Classification, disease and
  detection of parasites (cont’d)
– Cysticercosis (T. solium larvae)
  • Disease -Ccysts throughout the body tissues.
  • Transmission - Ova are ingested;
  • Detection - Serology, also x-ray, ultrasound, and
    other methods to detect mass lesions.
   Classification, disease and
  detection of parasites (cont’d)
– Trematodes "Flukes".
  • Leaf shaped, Hermaphrodite, Primitive gut,
    Suckers for attachment.
  • Life cycle: Definitive Host (contains adult
    wormova)
– Ova (Environment) consumed by 1st
  Intermediate Host(IH), becomes larva, and
  then 1st IH consumed by 2nd Intermediate
  Host and larva develops further, eaten by
  definitive host and develops into an adult,
  which produces more ova…
     Classification, disease and
    detection of parasites (cont’d)
• Pathogens - Schistosoma spp.
  (schistosomiasis).
• Disease - Effects of inflammation,
  hematuria.
• Transmission - Penetration of skin .
• Detection - Ova in stool/urine depending
  on species of schistosome.
     Classification, disease and
    detection of parasites (cont’d)
• Nematodes - Round worms”
  – Separate sexes, GI tract.
    • Pathogens: e.g. Ascaris lumbricoides
    • Some are adapted to attach to gut wall, e.g.
      Hookworms.
   Classification, disease and
  detection of parasites (cont’d)
– Nematodes (roundworms)
  • Disease - Abdominal pain/discomfort (most found
    in the gut).
  • Transmission - Fecal-oral via ova in stool.
  • Detection
     – Recognition of ova using stool microscopy.
     – Identification of adult worms.
   Classification, disease and
  detection of parasites (cont’d)
– Hookworms
  • Disease - Chronic blood loss.
  • Transmission - Larvae penetrate skin.
  • Detection - Identification of ova or larvae in stool.
    Classification, disease and
   detection of parasites (cont’d)
– Filaria - filariasis
   • Disease - Fevers, elephantiasis, swelling and
     deformity of limbs, genitalia.
   • Transmission - Mosquito borne.
   • Detection - Marasites (microfilaria) stained on
     blood film.
         Classification, disease and
        detection of parasites (cont’d)
•       Ectoparasites
    –       Colonize the body vs. Micropredators that
            bite only.
        •     Insects - ( 6 legs) - fleas, head-, body- and
              pubic lice (singular – Louse)
        •     Arachnida - ( 8 legs, but can have 6 in immature
              form) - ticks, mites
    –       Their importance is as vectors of disease
            and to a lesser extent cosmetic.
Adaptations to a parasitic existence
• Loss of structures or enzymes, e.g. GI tract.
• Development of pathogenic adaptations, e.g.
  mechanisms of attachment (hookworms).
• Defense mechanisms, e.g. resistance to
  digestion (nematodes).
• Increased reproductive capacity, eg. Ascaris.

Some parasites require infection of a host to complete their
lifecycles.
Other parasites may be free living in the environment and do
not need to cause infection to persist.
        Detection of GI protozoa –
          amoebae / flagellates
• Stool mixed with parasite preservative,
  e.g. SAF (formalin based).
• Microscopic identification of organisms
  from a concentrated extract of stool.
• Microscopic identification of organisms
  using a stained slide made from a filtered
  stool suspension.
  Note: Parasite preservative kills all organisms; therefore, a
  preserved specimen cannot be used for culture.

				
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posted:4/6/2010
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